17 research outputs found

    Probing gluon polarization with pi0's in longitudinally polarized proton collisions at the RHIC-PHENIX experiment

    Full text link
    This report presents double helicity asymmetry in inclusive π0\pi^0 production in polarized proton-proton collisions at a center-of-mass energy (s\sqrt{s}) of 200 GeV. The data were collected with the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC) during the 2004 run. The data are compared to a next-to-leading order perturbative quantum chromodynamic (NLO pQCD) calculation.Comment: 4pp. To appear in the proceedings of 16th International Spin Physics Symposium (SPIN 2004), Trieste, Italy, 10-16 Oct 200

    Exploring the polarization of gluons in the nucleon

    Get PDF
    We give an overview of the current status of investigations of the polarization of gluons in the nucleon. We describe some of the physics of the spin-dependent gluon parton distribution and its phenomenology in high-energy polarized hadronic scattering. We also review the recent experimental results.Comment: 10 pages, 13 figures. Talk presented at the "Second Meeting of the APS Topical Group on Hadronic Physics", Nashville, Tennessee, October 22-24, 2006. Reference adde

    Centrality dependence of charged hadron production in deuteron+gold and nucleon+gold collisions at sqrt(s_NN)=200 GeV

    Full text link
    We present transverse momentum (p_T) spectra of charged hadrons measured in deuteron-gold and nucleon-gold collisions at \sqrts = 200 GeV for four centrality classes. Nucleon-gold collisions were selected by tagging events in which a spectator nucleon was observed in one of two forward rapidity detectors. The spectra and yields were investigated as a function of the number of binary nucleon-nucleon collisions, \nu, suffered by deuteron nucleons. A comparison of charged particle yields to those in p+p collisions show that the yield per nucleon-nucleon collision saturates with \nu for high momentum particles. We also present the charged hadron to neutral pion ratios as a function of p_T.Comment: 330 authors, 15 pages text, 16 figures, 3 tables. Submitted to Phys. Rev. Lett. v2 has minor changes to reflect revisions during review process. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm

    High-pT pi^zero Production with Respect to the Reaction Plane in Au + Au Collisions at sqrt(s_NN) = 200 GeV

    Full text link
    Measurements of the azimuthal anisotropy of high-\pT neutral pion neutral pion production in Au+Au collisions at sqrt(s_NN) = 200 GeV by the PHENIX experiment are presented. The data included in this paper were collected during the 2004 RHIC running period and represent approximately an order of magnitude increase in the number of analyzed events relative to previously published results. Azimuthal angle distributions of pi^0s detected in the PHENIX electromagnetic calorimeters are measured relative to the reaction plane determined event-by-event using the forward and backward beam-beam counters. Amplitudes of the second Fourier component (v_2) of the angular distributions are presented as a function of pi^0 transverse momentum p_T for different bins in collision centrality. Measured reaction plane dependent pi^0 yields are used to determine the azimuthal dependence of the pi^0 suppression as a function of p_T, R_AA (Delta phi,p_T). A jet-quenching motivated geometric analysis is presented that attempts to simultaneously describe the centrality dependence and reaction plane angle dependence of the pi^0 suppression in terms of the path lengths of hypothetical parent partons in the medium. This set of results allows for a detailed examination of the influence of geometry in the collision region, and of the interplay between collective flow and jet-quenching effects along the azimuthal axis.Comment: 344 authors, 35 pages text, RevTeX-4, 24 figures, 8 tables. Submitted to Physical Review

    ϕ\phi meson production in dd++Au collisions at sNN=200\sqrt{s_{_{NN}}}=200 GeV

    Full text link
    The PHENIX experiment has measured ϕ\phi meson production in dd++Au collisions at sNN=200\sqrt{s_{_{NN}}}=200 GeV using the dimuon and dielectron decay channels. The ϕ\phi meson is measured in the forward (backward) dd-going (Au-going) direction, 1.2<y<2.21.2<y<2.2 (2.2<y<1.2-2.2<y<-1.2) in the transverse-momentum (pTp_T) range from 1--7 GeV/cc, and at midrapidity y<0.35|y|<0.35 in the pTp_T range below 7 GeV/cc. The ϕ\phi meson invariant yields and nuclear-modification factors as a function of pTp_T, rapidity, and centrality are reported. An enhancement of ϕ\phi meson production is observed in the Au-going direction, while suppression is seen in the dd-going direction, and no modification is observed at midrapidity relative to the yield in pp++pp collisions scaled by the number of binary collisions. Similar behavior was previously observed for inclusive charged hadrons and open heavy flavor indicating similar cold-nuclear-matter effects.Comment: 484 authors, 16 pages, 12 figures, 6 tables. v1 is the version accepted for publication in Phys. Rev. C. Data tables for the points plotted in the figures are given in the paper itsel

    Cold Nuclear Matter Effects on J/Psi as Constrained by Deuteron-Gold Measurements at sqrt(s_NN) = 200 GeV

    Full text link
    We present a new analysis of J/psi production yields in deuteron-gold collisions at sqrt(s_NN) = 200 GeV using data taken by the PHENIX experiment in 2003 and previously published in [S.S. Adler et al., Phys. Rev. Lett 96, 012304 (2006)]. The high statistics proton-proton J/psi data taken in 2005 is used to improve the baseline measurement and thus construct updated cold nuclear matter modification factors R_dAu. A suppression of J/psi in cold nuclear matter is observed as one goes forward in rapidity (in the deuteron-going direction), corresponding to a region more sensitive to initial state low-x gluons in the gold nucleus. The measured nuclear modification factors are compared to theoretical calculations of nuclear shadowing to which a J/psi (or precursor) break-up cross-section is added. Breakup cross sections of sigma_breakup = 2.8^[+1.7_-1.4] (2.2^[+1.6_-1.5]) mb are obtained by fitting these calculations to the data using two different models of nuclear shadowing. These breakup cross section values are consistent within large uncertainties with the 4.2 +/- 0.5 mb determined at lower collision energies. Projecting this range of cold nuclear matter effects to copper-copper and gold-gold collisions reveals that the current constraints are not sufficient to firmly quantify the additional hot nuclear matter effect.Comment: 453 authors from 59 institutions, 15 pages, 13 figures, 5 tables. Submitted to Physical Review C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.htm

    Systematic Studies of Elliptic Flow Measurements in Au+Au Collisions at sqrt(s_NN) = 200 GeV

    Full text link
    We present inclusive charged hadron elliptic flow v_2 measured over the pseudorapidity range |\eta| < 0.35 in Au+Au collisions at sqrt(s_NN) = 200 GeV. Results for v_2 are presented over a broad range of transverse momentum (p_T = 0.2-8.0 GeV/c) and centrality (0-60%). In order to study non-flow effects that are not correlated with the reaction plane, as well as the fluctuations of v_2, we compare two different analysis methods: (1) event plane method from two independent sub-detectors at forward (|\eta| = 3.1-3.9) and beam (|\eta| > 6.5) pseudorapidities and (2) two-particle cumulant method extracted using correlations between particles detected at midrapidity. The two event-plane results are consistent within systematic uncertainties over the measured p_T and in centrality 0-40%. There is at most 20% difference of the v_2 between the two event plane methods in peripheral (40-60%) collisions. The comparisons between the two-particle cumulant results and the standard event plane measurements are discussed.Comment: 347 authors, 27 pages text, RevTeX-4, 24 figures, 10 tables. Submitted to Physical Review

    Nuclear effects on hadron production in d plus Au collisions at root S-NN=200 GeV revealed by comparison with p plus p data

    Get PDF
    PHENIX has measured the centrality dependence of midrapidity pion, kaon, and proton transverse momentum distributions in d+Au and p+p collisions at root s(NN) = 200 GeV. The p+p data provide a reference for nuclear effects in d+Au and previously measured Au+Au collisions. Hadron production is enhanced in d+Au, relative to independent nucleon-nucleon scattering, as was observed in lower energy collisions. The nuclear modification factor for (anti)protons is larger than that for pions. The difference increases with centrality but is not sufficient to account for the abundance of baryon production observed in central Au+Au collisions at the BNL Relativistic Heavy Ion Collider (RHIC). The centrality dependence in d+Au shows that the nuclear modification factor increases gradually with the number of collisions encountered by each participant nucleon. We also present comparisons with lower energy data as well as with parton recombination and other theoretical models of nuclear effects on particle production

    The p38-Mediated Rapid Down-Regulation of Cell Surface gp130 Expression Impairs Interleukin-6 Signaling in the Synovial Fluid of Juvenile Idiopathic Arthritis Patients

    No full text
    Objective. Interleukin-6 (IL-6) signaling plays an important proinflammatory role, but this role is restricted by regulatory mechanisms that, for example, reduce the cell surface availability of the signaltransducing chain of the IL-6 receptor, gp130. The aim of this study was to determine whether the inflammatory environment in arthritic joints has an impact on monocytic gp130 surface expression and the extent to which regulatory processes in the synovial fluid (SF) can be reproduced in an in vitro model. Methods. Flow cytometry and live cell imaging were used to measure the cell surface expression and internalization of gp130. STAT-3 phosphorylation was monitored by flow cytometry and Western blotting. Results. In patients with juvenile idiopathic arthritis (JIA), levels of cell surface gp130 expression in SF monocytes were reduced compared to those in peripheral blood (PB) monocytes. These reduced levels were reproduced when PB monocytes from healthy donors were stim ulated with SF, and this reduction was dependent on p38 MAPK. The induction of p38 by IL-1 in PB monocytes interfered with IL-6 signaling due to the reduced cell surface expression of gp130. Conclusion. These results suggest that p38- mediated proinflammatory stimuli induce the downregulation of gp130 on monocytes and thus restrict gp130-mediated signal transduction. This regulatory mechanism could be of relevance to processes in the inflamed joints of patients with JIA
    corecore